Sterilization methods which use plasma are effective for sterilizing medical devices and the like.
Known plasma sterilization methods include sterilization treatment that involves using hydrogen peroxide and converting it to a plasma. However, hydrogen peroxide is a liquid at room temperature, and the introduction of a liquid into a low-pressure plasma chamber complicates both the structure of the apparatus and pressure regulation. Moreover, hydrogen peroxide is expensive, and so the high costs incurred by its use pose an additional challenge. Also, because hydrogen peroxide is an irritant, accidents (burns) due to the leakage or scattering of liquid are a constant concern.
Hence, the use of an oxygen-containing gas mixture has been disclosed in Patent Document 1 below as a substitute for hydrogen peroxide. However, reliably sterilizing an object with a gas mixture that has been converted to plasma is difficult, and it has not been possible to achieve adequate sterilization effects in this way. Also, increasing the number of gases used has made the construction of the apparatus more complex. Patent Document 2 below, which was disclosed in light of such circumstances, relates to the use of an oxygen-based gas alone rather than a gas mixture.    Patent Document 1: Japanese Patent Publication No. 2774193    Patent Document 2: Japanese Unexamined Patent Publication No. 2004-267524